As demand for information services has increased over the last decade, technical improvements have occurred in order to meet the demand. Approximately ten years ago a modem, typically at that time a commercial product, provided data transfer rates of around 2.4 kilobits per second ("KBPS") over an analog telephone line. Currently high-speed modems or ISDN terminal adapters coupled over a public switched telephone network provide data transfer rates of between 28.8 and 128 KBPS for both commercial and residential customers. Internet service providers are currently seeking technology that will furnish customers with faster transfer rates for reducing download time. In addition the evolution of digital television and other video developments have increased the demand for even higher data transfer rates, such as for example, several megabits per second ("MBPS"). These higher data transfer rates are sometimes called "broadband service" or MBPS service. The MBPS service typically provides for both upstream and downstream data transfer and may be referred to as interactive broadband service ("IBS"). An example is asymmetric digital subscriber line ("ADSL") service over twisted pair wires of the telephone companies, where the down stream rates may be 6 MBPS and the upstream rates may be around 1 MBPS.
The 1996 Telecommunications Deregulation Act encouraged a variety of providers to compete for IBS. The providers currently considered as leaders in meeting the IBS needs of consumers include long distance carriers, local phone companies, and cable companies. In order to provide IBS, resource sharing and partnerships may develop among a variety of businesses.
There are currently four technologies being considered as contenders to provide IBS or similar service. These technologies include methods for using the existing twisted pairs of wires in the telephone network, coaxial cables, fiber links, and wireless links. In some cases a mixture of these technologies may be used to provide IBS. A detailed discussion of these technologies can be found in the IEEE Network Magazine, Special Issue on Broadband Services to the Home, Vol. 11, No. 1, January/February, 1997. Each of these technologies shows promise towards providing IBS, but each technology has technical problems and economic constraints. An access network that can provide for a complex mix of broadband services such as a high-speed internet connection, video on demand, telecommuting, and future applications is currently being developed incorporating these four technologies. Selection of the best or optimum technology is dependent on a variety of parameters such as the infrastructure of a country, the physical environment for a new installation, the demographic diversity of users and other factors.
Although the above four technologies are expected to provide IBS to a large number of subscribers, new technologies may be capable of providing IBS technology. Currently a partnership exists between local telephone service providers and power companies. In a typical residential location, a support pole or telephone pole, is used as part of the structure for providing both power lines and telephone lines to a customer. Cable television ("CATV") providers recently joined the partnership in order to have support poles for coaxial cables. Because of recent asymmetric digital subscriber line development, some local telephone companies may be able to deliver television programming over existing and new telephone lines. Further it has been discovered that part of the excess bandwidth on television cables of CATV companies can be used to provide telephone and data service.
As power companies look for new uses of the power system network and demands for data bandwidth increase, the use of power system networks may be a means for providing IBS. Currently, existing power line communication systems are limited to low-speed data used for monitoring and controlling functions in the power system network. These existing systems are called power line carrier communication systems. Typically, power line carrier communications systems use conventional high-voltage transformers to couple communications signals to and from the high-voltage lines of a power system. The high-voltage transformers are expensive and typically limited to coupling signals having frequencies between 30 Hertz and 50 kilohertz. Some newer power line carrier systems, such as described by in U.S. Pat. No. 4,142,178, use high breakdown voltage capacitors to couple onto the high voltage lines and operate at frequencies up to about 300 kilohertz. These newer power line carrier communications systems use narrow bandwidth carriers and provide only low-speed data. Because of cost and data bandwidth limitations, present power line carrier communication systems are not suitable for providing IBS.
In order for a high-voltage cable to serve as communication channels for IBS there are a variety of problems to consider. For a high-voltage cable to provide high-speed data there must be an apparatus and method for converting data streams to a signal suitable for transmission over the high-voltage cables. Such an apparatus, method or system should not compromise the power delivery abilities of the power system. In addition, such an apparatus, method or system must be capable of operating with and adapting to a wide variation in communication channel impairments. Power delivery loads and particularly changes in loads must not affect the transmission of information on the high-voltage cable. In addition, such an apparatus must be inexpensive, small, environmentally acceptable, essentially maintenance free and easy to install in order to compete with contending technologies. Such an apparatus must also guarantee safety by isolating the communications function from the high-voltage power delivery at the customer's premise.